Cucurbits. James R. Myers
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cucurbits: the size of various plant parts increased; early female flower production was selected; seed dormancy was reduced; photoperiod response was eliminated; fruit bitterness was eliminated; and fruit flavour and appearance were improved.
Given the nature of cucurbits, it is not surprising that they are among the most ancient of cultivated plants. Archaeological evidence suggests a pantropical distribution for bottle gourd going back more than 10,000 years. Bottle gourd may have been cultivated in Asia, Africa and the New World at that time, or later if the oldest remains are of wild plants. Using molecular taxonomy, even older times can be seen, although humans did not exist then. Evidence of human use of cucurbits in the form of seeds or fruit rinds of Cucurbita pepo has been found at sites dating ca 10,000 bp in Mexico and ca 5000 bp in central USA (Smith, 1997a, 2006). Phytoliths are particles of silicon dioxide found in the cells of Cucurbita spp. These particles remain in soil samples and can be used as a diagnostic tool in archaeological studies of this genus. This technique has been used to document the presence of domesticated Cucurbita spp. in South America as early as 12,000 bp (Piperno and Stothert, 2003). Enlarged fruit parts indicate that other squash species were being cultivated for food in the New World by 7000 bp, if not earlier.
Cucumber (Cucumis sativus) is of Asiatic origin, with its primary centre of diversity in India and secondary in China. Although cucumber evolved from melon, the two species cannot be crossed. Cucumber can be crossed with Cucumis sativus var. hardwickii, C. s. var. sikkimensis and C. s. xishuangbannanensis. Also, Cucumis hystrix, a wild species with traits from both melon and cucumber, has been crossed successfully with cucumber. However, Cucumis setosus is a melon relative that looks like cucumber, but will not cross with it. Cucumber has been grown in Asia for several thousand years. The remains of Cucumis crops (melon or cucumber) in eastern Iran have been dated to the third millennium bc.
Melon (Cucumis melo) likely originated in India from C. trigonus or C. callosus (Sebastian et al., 2010). The Australian species C. picrocarpus has the highest DNA sequence similarity to C. melo. However, the oldest wild relatives of melon, such as C. hirsutus, C. humifructus and C. sagittatus, originated in Africa. Melon was grown in Egypt in the second millennium bc and in Iran during the third millennium bc. Humans moved the melon throughout the Middle East and Asia, making it an important vegetable in India, Egypt, Iran and China. Iran, Afghanistan and China are secondary centres of melon diversification. Spain is a tertiary centre of diversity.
Melon was one of the most important vegetables in ancient China, with archaeological remains there dating back to 5000 bp. The origin and domestication of melon is still debated, though evidence for two lineages have been described, with an Indian relative (C. trigonus) being the most closely related living relative to C. melo (Endl et al., 2018).
Watermelon (Citrullus lanatus) is an African native, and became important in northern Africa and southwestern Asia by 6000 bp. It is recorded in the Bible (Numbers 11:5) that the Jews missed the watermelons and cucumbers of Egypt during the Exodus in the 12th century bc. Probably, that passage refers not to cucumber but to snake melon, also known as Armenian cucumber. A watermelon relative, colocynth (Citrullus colocynthis), is probably the toxic fruit mentioned in the Bible in II Kings.
The uses of cucurbits are diverse. Fruit may be eaten when immature (e.g. summer squash) or mature (watermelon). They are baked (squash), fried (bitter gourd), boiled (wax gourd, snake gourd), stuffed (stuffing cucumber), pickled (cucumber, pickling melon), candied (watermelon, squash, wax gourd, Malabar gourd), consumed fresh in salads (cucumber) or as a dessert (melon, watermelon). Fresh fruit are sold soon after harvest or following a storage period of several weeks to months. Processing for long-term storage often involves canning, freezing, or pickling (Fig. 2.1). Juice from cucumber fruit is used to make salad dressing, lotion and shampoo. Watermelon fruit juice is used directly as a fresh drink, but results in a ‘squash flavour’ when pasteurized. Juice from the fruit of watermelon, Malabar gourd and other cucurbits is fermented to make alcoholic beverages; for example, a liqueur is made from melon in Japan. Fruit are the most important plant part that is used. However, seeds (Cucurbita, Cucumeropsis and many others), roots (chayote), flowers (squash) and leaves and shoot tips (Telfairia, Momordica) also provide human sustenance.
Fig. 2.1. Pickled snake melon.
Seeds of watermelon, oyster nut, !nara and other cucurbits are an important part of the African diet. Watermelon seeds are used to make snacks, using the large (long) seed size (not the medium, short or tomato seed sizes), usually with a white seed coat. In Mexico and Central American countries, squash seeds are sold in stores and at street corners as snacks. The development of squash and pumpkin cultivars with ‘naked’ seeds, devoid of tough seed coats, has increased the popularity of squash seeds for food in other countries.
Cucurbits are used for other purposes besides food and drink. From bottle gourds, people have fashioned storage containers, bottles, cups, bowls, utensils, smoking pipes, musical instruments, penis sheaths, masks, floats for fishnets, rattles for babies and many other items. The dry fruit rinds of other cucurbits, including wax gourd, wild and cultivated species of Cucurbita and fluted pumpkin, sometimes serve as containers and utensils as well. The oils extracted from seeds of watermelon, squash, luffa, antidote vine, lard plant, white-seeded melon, colocynth and other cucurbits are prepared for cooking, illumination, candle and soap manufacture and industrial purposes. Colocynth seeds have 18% oil (70% of which is linoleic). The fibrovascular system of a mature luffa fruit provides a sponge suitable for various purposes, including use as a filter. Nigerians pound and work the thick stems of sponge plant to yield white, absorbent fibres that serve as a washing sponge. Stem fibres of fluted pumpkin are extracted for use as a sponge and for making rope. Jewellery is fashioned from seeds of various cucurbits (Cayaponia kathematophora, Marah species). Squash flowers are used in make-up and cucumber fruit extracts are added to soap and shampoo. Arabs employ the dried fruit pulp of colocynth in the making of gunpowder, tinder and fuses.
Medicinal applications of cucurbits are numerous. Since ancient times, indigenous cultures worldwide have employed cucurbits to treat ailments. A Chinese medicinal text written during the 1st century ad mentions the therapeutic benefits of wax gourd, pickling melon, bottle gourd and Japanese snake gourd. In modern Chinese commerce, he zi cao (Actinostemma lobatum), jiao-gu-lan (Gynostemma pentophyllum), luo-han-guo (Siraitia grosvenorii) and species of Trichosanthes are the most important medicinal cucurbits (Yang and Walters, 1992; Cai et al., 2004; Xu, 2017).
Some of the reported therapeutic properties, including the use of cucurbits as purgatives, emetics and anthelmintics (anti-parasite drugs), are due to cucurbitacins, which are bitter triterpenoid compounds known to have drastic effects on the digestive system. Cucurbitacins are present in almost all cucurbits, usually throughout the plant, but especially in fruit and roots. Other toxic and potentially medicinal compounds in cucurbits include saponins, free amino acids and alkaloids.
Cucurbit fruit, and their extracts, are the plant part most commonly prepared for medicine. The gourd-like fruit of colocynth is used as a purgative for constipation and parasitic worms, as an anti-tumour agent for cancer and as a remedy for fever, urogenital disorders and other problems. The bitter roots of many cucurbits (e.g. bryony) have cathartic effects as well. Leaves are employed for medicine less frequently,